This invention relates to a method of forming electromagnetically shielded spaces which are formed in a building and in which communication is performed by using electric waves and, more particularly, to a method of forming electromagnetically shielded sections with respect to rooms in stories of a building by using electromagnetically shielding materials to form building structural members for outer walls, floors and so forth.
To transmit information between telephones and/or computers within a building, a wire communication system may be adopted, but it necessitates cable installation operations. The flexibility of this type of system with respect to layout changes or extensions is inadequate, and there are other various problems relating to application of this system. In particular, while the amount of information of communication increases with development of office automation in office buildings, there is a limitation of increase in the capacity of communication lines.
Recently, there is an increased tendency to adopt wireless communication systems using electric waves in buildings instead of wire communication systems. To use electric waves in a building, it is necessary to prevent leaks of electromagnetic wave noises to the outside, prevent extraneous electromagnetic wave noises from entering the building and causing malfunctions of the system and avoid electric wave interference.
In the case of advanced information processing using computers, there is a problem in terms of maintenance of secrecy. In particular, as a result of improvements in the electric wave receiving technology, a problem of leakage of secrete information has arisen; information leaking from computers in a building can be received from the outside by a high-sensitivity receiver.
For this reason, as wireless communication systems are increasingly adopted for communication inside buildings, means for forming part of a building or the interior of the building as an electromagnetically shielded space, e.g., those applied to intelligent buildings are regarded as effective in terms of prevention of leakage of information from data processors to the outside of the building.
In ordinary intelligent buildings, a mass of information communication equipment including a composite electronic switchboard and a computer is used in a common system to communicated information inside the building and between the inside and the outside of the building. For such a system, it is important to supply desired information rapidly while reducing the cost of dosing so since the amount of information to be communicated is being increased.
To construct an electromagnetically shielded space, electromagnetic shielding materials are used in outer structural members and members constituting openings such as windows, entrances and exits so that the whole of the building is constructed as an electromagnetically shielded structure, thereby enabling communication inside the building using electric waves. If, for electric wave communication inside a building, a frequency band for n channels is assigned for each of the stories of the building, and if the number of the stories is m, frequency bands for n.times.m channels are needed. If the frequency band width for each channel is 25 kHz, the total required frequency band for the electromagnetically shielded space corresponding to the whole of the building is 25 kHz.times.n.times.m. In consequence, there is a problem in that if the number of stories of the building is increased and if the traffic is increased, the required frequency band width (number of required channels) becomes wider and the scale of the communication facilities is increased correspondingly, resulting in an increase in the installation cost.
A method of electromagnetically shielding the stories from each other by providing floors and ceilings with electromagnetic shielding properties may be adopted in order that the same frequency bands can be simultaneously used in different ones of the stories to perform communication therein independently. Ordinarily, for formation of such electromagnetically shielded zones, conductive materials or members such as foils, metallic meshworks and conductive paints may be utilized as electromagnetic shielding materials at ceilings, floors and walls.
This method, however, entails a problem of a considerable reduction in the electromagnetic shielding performance because electric waves leak through even a small gap in the shielding structure and propagates from one side of the shielding to the other side. To improve the electromagnetic shielding performance, it is necessary to completely cover the periphery of each zone with an electromagnetic shielding material and to apply electromagnetic shielding materials over the whole of floors, walls and other structural members. It is inevitable that the cost of a building constructed in this manner is considerably higher than those of ordinary buildings.
Even if electromagnetic shielding materials are used for structural members of the building, the electromagnetic shielding performance of the resulting shieldings is usually reduced by some portions of the shieldings which are not easily seen. That is, it is possible that gaps are formed between portions of floors, columns and walls abutting against each other.
FIGS. 1(a) to 1(c) are diagrams illustrating a problem with respect to portions of a partition wall and a floor abutting against each other, FIGS. 2(a) and 2(b) are diagrams illustrating a problem with respect to portions of a partition wall and a ceiling abutting against each other, and FIG. 3 is a diagram illustrating a problem with respect to portions of a floor and an outer wall abutting against each other. In these figures, reference characters 61 and 73 denote partition walls; reference characters 62 and 71, concrete slabs; and reference characters 63, 76, and 83, decking plates. A reference character 64 denotes an electromagnetic shielding material; a reference character 72, a stud runner; a reference character 74, a plaster board; a reference character 81, an aluminum curtain wall; and a reference character 82, a glass opening. Reference characters 75 and 84 denote asbestos spraying bed laths.
Ordinarily, a partition wall needs to have fire protection properties and sound insulation properties and is formed of concrete, dry fire-proof board, CB blocks or ALC. If the partition wall 61 is formed of such a material, an electric wave B passes through the partition wall 61, as shown in FIG. 1(a). To enable electromagnetic shielding performance, electromagnetic shielding material 64 is applied to one side of the partition wall 61, as shown in FIG. 1(b). In this structure, however, the concrete slab 62 has no electromagnetic shielding properties while the metallic decking plate 63 has electromagnetic shielding properties, and the electric wave therefore propagates from one side of the shielding to the other side via a portion of the floor 62 on the decking plate 63 below the lower end of the partition wall 61, as shown in FIG. 1(c), resulting in a reduction in the electromagnetic shielding performance.
There is a similar problem with respect to an upper end portion of a partition wall and a portion of the decking plate of a floor slab connected to each other. Referring to FIGS. 2, at corresponding connecting portions, asbestos spraying bed lath 75 for sound insulation is usually stretched on the stud runner 72 through the depth H of the decking plate 76, as shown in FIG. 2. The type of connection between these portions varies depending upon the shape of the decking plate 76, and the connection tends to become complicated. For this reason, the electromagnetic shielding effect is usually inadequate at such connections, and electric waves propagate through a connecting portion of a partition wall between an electromagnetically shielded zone and a non-shielded zone, resulting in a reduction in the electromagnetic shielding performance.
A similar problem exists with respect to connection between a floor and an outer wall member. Spaces formed at the connection between a floor (decking plate 83) and an outer wall member are filled with a flexible member such as asbestos spraying bed lath 84 without using a solid material such as concrete in consideration of deformation of the outside surface of the curtain wall caused by, for example wind pressure as well as need for an ordinary fire protection partition. However, as shown in FIG. 3, the connection between the deck plate 83 and the outer wall member entails a similar problem of leaks of electric waves. There is also a problem of interference between electric waves in the case where independent electromagnetically shielded zones are formed in adjacent stories. Electric waves also leak through a gap between a column and a floor.
Thus, the electromagnetic shielding effect is reduced at connections between structural members constituting walls, floors and ceilings, although each structural member has electromagnetic shielding properties. The efficiency with which the electromagnetic shielding is constructed is small while the cost of the structural members is increased to obtain electromagnetic shielding properties.
Also, in the case where electromagnetic shielding sections are respectively formed in different stories as described above, there is a problem in that an air conditioning machine room and electricity shafts in the core are regarded as noise sources with respect to office rooms and that electric waves in adjacent stories interfere with each other by propagating via the core section. In consequence, even if electromagnetically shielded sections are respectively formed in stories by forming ceiling and floors having electromagnetic shielding properties, an additional means to cope with such a problem by, for example, respectively shielding office rooms is needed. To solve this problem, an electromagnetic shielding structure which encircles the air conditioning room and electric shafts on all sides is ordinarily adopted, and, further, a type of electromagnetic shielding structure in which shielded sections are completely closed at partitions and other members is adopted.
However, the construction cost becomes very high if each of ordinary office rooms is enclosed in such an electromagnetic shielding structure including doors and the like. This construction is also disadvantageous in terms of functions and appearance of offices.